1. Technical Field
The invention relates generally to memory fabrication, and more particularly, to methods for enhancing trench capacitance and a trench capacitor so formed.
2. Background Art
Capacitance enhancement is essential for trench technology scaling. There are a variety of techniques to increase a surface area of trenches to increase capacitance. In one approach, the trench is formed in a bottle shape to increase the surface area. This approach, however, requires a sacrificial collar, and is susceptible to trench merging. The bottle shape approach also requires extra process steps. In another approach, hemispherical silicon grains (HSG) are formed on a sidewall of the trench to increase its surface area. This approach also requires a sacrificial collar and extra process steps, and further, narrows the trench. Use of new high dielectric constant materials (such as aluminum oxide or hafnium oxide) has also been proposed, but this approach requires new materials and presents numerous integration issues. It is therefore desired to have a capacitance enhancement without adding process complexity and cost.